We have recently discovered a new property of muscle cells. This new property is a steady electric current that leaves the cell near the end plate (synaptic) region and reenters the cell in the flanking regions. This electric current was discovered with a relatively new recording device, a vibrating microelectrode which can detect very small electric currents flowing in the extracellular fluid. The experiments described in this proposal are designed to study this membrane current in more detail The validity of the extracellular current measurements made with the vibrating electrode will be tested. The major goal of the grant will be to characterize and determine the physiological basis of the endogenous current; ionic conductances and ion pumps will be studied since regional variations in these could generated the endogenous current. Finally, the endogenous current and the electric field may have some physiological aoles; since the field is focused at the synapse, it may be important for the formation and maintenance of synaptic connections.